This invention relates to photographic film elements, and particularly to transparent photographic film elements having an improved anchoring substratum (commonly known as a subbing or "sub" layer) between the film base and the water-permeable colloid layer or layers disposed thereon.
It is common practice in the manufacture of photographic films to employ as a film support a dimensionally stable biaxially oriented heat set polyester such as polyethylene terephthalate. Polyethylene terephthalate films are conventionally prepared, for example, by catalytic ester-interchange reaction between dimethylterephthalate and ethylene glycol, followed by catalytic polymerization under vacuum of the resulting dihydroxyethylene terephthalate monomer. The final polymer is then cast as a film, biaxially oriented by stretching, and heat set. Films made in this manner have a relatively hydrophobic surface, and do not adhere well to hydrophilic coatings containing gelatin. Accordingly, it is customary to employ several intermediate layers between the support and the photographic emulsion layer in order to effect suitable adhesion between the two. Generally, two intermediate layers are used. The first is a chlorine-containing copolymer resin coating applied to the polyester support after the latter has been cast into film but before it has been stretched to obtain the desired biaxial orientation and heat set. This resin coating provides good adhesion to the polyester, and at the same time provides good adhesion to the second subbing layer, which is applied after stretching and heat setting. This second layer is usually composed of a hydrophilic colloid such as gelatin, which in turn adheres well to the gelatin-containing photographic emulsion layer. Before applying the photographic emulsion layer, the dual-subbed polyester support is heat-relaxed to achieve dimensional stability.
The trouble with this system is that a certain amount of scrap film is formed in the process of biaxial orientation and heat setting of the polyester film, and it cannot be recycled because the first subbing layer has already been applied, and it is incompatible with the composition of the recycle. This prevents recycle of the polyester film unless the first subbing layer is removed beforehand, and its removal is costly and difficult, making this undesirable. As a result much film has to be discarded instead of being recycled. The present invention provides a solution to this problem.